Mechanical clamps are commonly used in manufacturing processes to clamp a workpiece in place and to secure the workpiece while the workpiece is being machined, welded or otherwise worked.
An example of prior art mechanical clamp apparatus is shown in the U.S. Pat. No. 2,537,594, issued Jan. 9, 1951 and in the U.S. Pat. No. 2,236,439 issued Mar. 25, 1941.
One of the features of the common prior art clamps is that they require adjustment in order to clamp workpieces of differing thicknesses. It is common that the thickness of the workpiece in many applications may vary from one workpiece to the next such that adjustment of the clamp is required for each workpiece if uniform clamping pressure is to be applied. Additionally, in normal practice a plurality of mechanical clamps are required to support each workpiece and adjustment of each one of these clamps is required if workpieces of different dimensions are being clamped.
The mechanical clamps of the type shown in the Lehmann and McKenna patents are intended to be useful to clamp workpieces of varying thicknesses without adjustment of the clamp. For example, these clamps can accommodate workpieces which vary in thickness by as much as approximately 1/16 inch. However, these clamps apply varying clamping forces on the workpiece depending on the thickness of the workpiece. This variation in clamping pressure can result in bending or distortion of the workpiece.
Mechanical clamps of the type of the invention have also included hydraulic or pneumatic motors for applying clamping force. While pneumatic clamps are desirable because compressed air is readily available in many manufacturing facilities, and pneumatic fluid motors employed by the prior art clamps are useful where low clamping forces are sufficient, the pneumatic mechanical clamps of the prior art do not generate sufficient clamping force to be useful in many applications. Hydraulically driven clamps can generate greater clamping forces, but these devices are expensive because they require hydraulic fluid or the combination of pneumatic and hydraulic cylinders.
Attention is also directed to the U.S. Pat. No. 3,482,830 issued Dec. 9, 1969; the U.S. Pat. Nos. 3,381,954; 3,273,878 and 2,972,476 and the U.S. Pat. Nos. 3,302,943 and 3,347,542.